When transporting speech in packet switched communications systems, such as systems operating under ATM (Asynchronous Transfer Mode) or by Internet Protocol (IP) techniques, warping of the time scale occurs from different transportation or transmission delays of the different packets, and buffering. In practice, each speech burst may encounter an individual transmission delay.
For objectively measuring the speech quality of time warped speech signals, such as signals transmitted in VoIP (Voice over Internet Protocol) systems, by comparing corresponding speech bursts of the output speech signal and its original input speech signal, the time relation between the speech bursts has to be determined before a performance estimate of the output speech signal can be provided.
In the context of the present invention, the term “speech burst” has to be construed as an amount of speech delimited by periods of lower energy or loudness. For the purpose of the present invention, the term speech burst refers to a speech utterance either on a coarse or sentence level or on a fine or spurt level.
Applicants' International patent application WO 96/06496 (invented by Michael HOLLIER et al, titled Analysis Of Audio Quality and filed Aug. 17, 1995) discloses a method of analyzing speech quality of an output speech signal affected by time warping in a communications system. Continuous time dewarping is applied to the received output signal using transform or digital filtering techniques, to adapt the macro properties of each speech element, such as pitch and duration, for providing an estimated original input signal. The estimated original input signal and the actual output signal received are subjected to a comparison step for providing an estimate of the subjective audio perception quality.
In a VoIP system, for example, warping is a discontinuous phenomenon in that the signals are manipulated during periods of silence, to keep the manipulations essentially non-audible to the receiver (i.e. the person receiving the signals). Degradation of the speech signal by discontinuous warping cannot be accounted for by the method disclosed in Applicants' International patent application WO 96/06496 (Michael HOLLIER et al, entitled “Analysis Of Audio Quality” and filed Aug. 17, 1995).